1. Field of the Invention
The present invention relates in general terms to a system for the treatment of a body duct and process for its manufacture.
The invention applies mainly to the field of treatment of blood vessels having stenoses or aneurysms and more generally to the field of the treatment of various anatomical ducts of the human or animal body, such as, for example, the urinary ducts and especially the urethra, the digestive ducts and especially the oesophagus, or even the respiratory ducts and especially the trachea.
2. Description of the Related Art
The narrowing of the body ducts and especially the blood ducts (vessels, arteries or veins) are the origin of serious disorders, and various techniques have been developed to prevent such complaints.
Within the context of the treatment of a stenotic blood vessel, the conventional technique, referred to as angioplasty, concerns the use of a dilatation catheter, which has on its distal extremity an inflatable expanding element, referred to as a balloon or balloon-tip. This dilatation catheter is introduced into the interior of the artery, and when the balloon is positioned at the level of the stenosis, the balloon is then inflated to a relatively high pressure, in such a way as to compress the stenosis in the wall of the artery and to thus restore the normal passage cross-section of said artery at the location of the stenosis.
More and more, this conventional angioplasty technique is accompanied or completed by the percutaneous implantation, in the interior of the stenotic vessel, a device, commonly designated by the American term "stent", for preventing the dilated vessel from spontaneously closing up again or for preventing its occlusion by the formation of a new atheromatous plaque and the possible recurrence of stenosis.
Stents are generally divided into two major categories.
So-called auto-expandable stents are capable of changing by themselves from a first, constricted position, of reduced diameter, enabling them to be guided through the body duct, to a second, expanded working position.
These devices can be made from a material of recovery capacity, or even be shaped so as to possess an "internal elastic recovery capacity" enabling them to change from a first, constricted position under stress, to a second, expanded working position.
The second category of stents consists of devices whose expansion can be forced mechanically, generally under the effect of a force exerted from the inside outwards in a radial direction, such as, for example, the force exerted during the inflation of a balloon disposed inside said stent.
Such devices are generally made of materials with a low elastic recovery capacity which are capable of undergoing an irreversible plastic deformation.
This type of stent is currently the most commonly employed, in particular because it is easier to implant than the above-mentioned auto-expandable stents.
Hitherto, the devices belonging to this second category of stents are constituted of a tubular frame of reduced diameter of shape corresponding to the shape desired in the stressed position.
The deformation of these devices, under the effect of the inflation of the balloon, causes their radial expansion but is accompanied by a decrease in length. Such known devices in general also lack longitudinal flexibility.
Furthermore, it has been observed that the expansion of these known devices does not take place in a regular manner, their symmetry not being itself sufficient to distribute the forces of deformation acting on it during the inflation of the balloon.
The irregular expansion of these devices, due notably to the absence of distribution of the radial forces acting on it, results notably in it not being possible to obtain a passage of constant dimension in the body duct, and from this, this type of device is not entirely satisfactory.
The irregular expansion of these devices is also due to the fact that during the inflation of the balloon, the balloon has a tendency to first of all inflate at its ends, thus causing a compression of the stent in the longitudinal direction.
Finally, it has been observed in these known devices that the stent forming element is not always maintained on the balloon during the inflation and consequently risks shifting during intervention.